It has heretofore been proposed to supply fuel to an internal combustion engine by means of a pressure-controlled electric-motor fuel pump and a one-way or non-return fuel line that connects the pump to the fuel injectors at the engine. For example, U.S. Pat. No. 5,044,344 discloses a fuel delivery system in which a fuel pump is responsive to application of electrical power for supplying fuel under pressure from a supply or tank to the fuel injectors at the engine. A check valve is positioned in the fuel line between the pump outlet and the injectors for preventing reverse flow of fuel from the engine injectors to the pump. A pressure sensor is operatively coupled to the fuel line between the pump outlet and the check valve, and is coupled to electronic circuitry for applying electrical energy to the pump motor as a function of pressure in the fuel line. A pressure relief valve is connected to the fuel line between the check valve and the engine for returning fuel from the line to the supply in the event of over-pressure in the fuel line.
Although the fuel delivery system so disclosed addresses and overcomes a number of problems theretofore extant in the art, further improvements remain desirable. For example, a problem is encountered in pressure-controlled pump systems of the described character in situations where fuel demand at the engine decreases such as during a period of engine deceleration, and thereafter rapidly increases such as when rapid acceleration is demanded by the operator. During the period of low fuel demand at the engine, a low level of pump operation is all that is necessary to maintain desired fuel pressure in the fuel line. However, when demand is rapidly increased, the fuel pump often cannot accelerate operation sufficiently quickly to satisfy the demand.
Another problem extant in the art involves fuel vaporization in the fuel line at very high temperatures. For example, fuel rail temperature tends to increase significantly after the engine is turned off and coolant system operation terminates. The fuel may vaporize in the rail and injector area, particularly when ambient temperature is relatively high. This may cause difficulty in restarting the engine and/or unstable idling performance.
It is therefore a general object of the present invention to provide a fuel delivery system for internal combustion engines in which the fuel pump motor is operated as a function of fuel line pressure while at the same time maintaining a minimum level of pump operation in low fuel demand situations so as to increase the ability of the pump to respond to a subsequent high fuel demand. Another object of the present invention is to provide an engine fuel delivery system of the described character that substantially reduces or prevents vaporization of fuel in the fuel line even under high operating temperature conditions.